Glass doors- Home depot carries inexpensive glass doors off the shelf. Add them every where you can to create the illusion of more light and space. You can even add them to the bathroom, just add frosted glass.
#bldgproductoftheday I am in love with these beautiful dark wood interior doors from Appalachian Woodwrights! Very classic design, and it looks like they have pocket versions as well. Great way to step up a home's interior.